Risk and Pollutant Protective Concentration Levels of Drilling Waste Used to Pave Oil and Gas Field Well Sites

Paving oil and gas field well sites of drilling waste allow us to reuse solid waste. However, to keep the risk within acceptable limits, some questions need to be answered: what is the dilution effect that soil and groundwater have on the transport of pollutants? What is the minimum concentration of pollutants leached from drill wastes? In this study, we focus on the paving of well sites using drilling wastes, and we analyze the pollutant migration pattern in the soil vadose zone and groundwater mixing zone after rainwater leaching. The drilling waste pollutant protective concentration level (PCL) and the corresponding dilution attenuation factor (DAF) were then proposed. In addition, the PCL’s accessibility, uncertainty, and environmental significance were further analyzed. It was found that the pollutant dilution factor (DF) of the groundwater mixed zone was strongly influenced by the thickness of the mixed zone, the groundwater Darcy rate, the length of the contaminant source, and the permeability, and each contributed approximately 25%. The soil vadose zone attenuation factor (AF) was primarily influenced by the soil vadose zone (i.e., groundwater depth) thickness that contributed approximately 53%. The contaminant DAF values of the well site drilling waste paving (e.g., the soil vadose zone thickness ranged from 5 to 30 m) ranged from 12 to 84. Additionally, the PCL values of the contaminants ranged from 12 to 84 times of the acceptable concentration (e.g., the Class III permissible limits of the Groundwater Quality Standards GB/T 14848-2017) at the groundwater compliance point. The expression for the exponential relationship between the DAF or PLC and the depth of the soil vadose zone was also provided in this study. The study results provide a reference for the actual process of the use of drilling wastes to pave well sites and for solid waste treatment or soil remediation decision-making and the associated risk assessment procedures.